This invention relates to the copying lens that is used at the magnification of one to one and thereabout and has a reflection surface.
With the recent spread in usage of copying machines, a copying lens with symmetrical structure that is divided at its symmetrical surface, and in which said symmetrical surface serves as a reflection surface, has widely been used in order to reduce the total size of the machine and lens cost; furthermore a copying lens with a reflection surface in which the symmetrical surface has a radius of curvature has been actively developed recently.
In the publicly-known lens system of such a form, for example in the lens system described in the specification of Japanese Patent Examined Publication No. 25734/1977 or of Japanese Patent Publication Open to public Inspection No. 66257/1975, the total length of the lens (the length from an apex of the first surface to an apex of a reflection surface) is more than 0.19 f against the composite focal length f of the lens and therefore it has not necessarily satisfied the requirement for the development of a smaller and less expensive lens.
With constant F number and angle of view, if it is possible to make the total length of the lens short, it is inevitably possible to make the lens diameter small, and the reduction in total length and diameter naturally leads to the saving of lens material and less processing fees.